Distortion viewing is a commonly used visualization technique that shows an area of interest, the focus, which is part of a larger image, the context. The focus is shown magnified, while some distorted representation of the immediate context is retained, approximately in-place around the focus. The development of distortion viewing was partly inspired by photographic fish-eye lenses and optical magnifying lenses [1, 2]. Focus+context is an in-place (distorted) spatial visualization method, as opposed to overview+detail, which is a spatially separated (undistorted) method, and zooming, which separates related (undistorted) views in time [3].
One problem with interactive distortion viewing is the difficulty of focus targeting [4], a term used to describe the placement of the focus exactly where intended. The problem arises because increasing magnification renders control more difficult, and the maximum magnification appears exactly at the point of interest in the middle of the focus. This difficulty may be viewed as a variant of a general trade-off between speed and accuracy that also appears in other related settings [5].
Methods of addressing the focus targeting difficulty include speed dependent auto zoom (SDAZ) [6], speed coupled flattening (SCF) [4], and three techniques introduced by Appert et al [2], which they call speed, key and ring.
Speed is related to SCF and SDAZ, while key and ring discretely change the slope of the C-D function on detection of a key press and on the cursor reaching the edge of the focus ring respectively.
Leung and Apperley [7] reviewed distortion-oriented presentation techniques up to 1994, including a table of one-dimensional transformation functions T and magnification functions M. Magnification is the first derivative of transformation and these functions are usually both normalized to the domain [0,1]. In a two-dimensional setting, T and M may be interpreted as radial functions T(r) and M(r).
The known methods for facilitating focus targeting in the context of distortion viewing are all based either on cursor speed, or on spatial discontinuities in the interpretation of cursor movements. Discontinuities may appear jarring to the user, and position is more suitable for some control applications than speed. Thus there remains a need in the art for a method that is both continuous everywhere and that depends on position only. The present invention is intended to fill this gap.